Previous work in our laboratory identified CHOP as an erythropoietin (Epo) regulated responsive protein. Using the yeast two-hybrid system, three clones of genes have been found to interact with CHOP in yeast and in vitro. One of the three was confirmed to interact with CHOP in vivo and identified to be FTE-1, a v-fos transformation effector gene. The objective of this proposal is to identify and characterize the other two genes and their protein products and to understand their roles in Epo regulated erythropoiesis. Complete sequencing analyses will be performed and full-length coding sequences will be obtained for these two genes. The mRNA levels of these two genes following Epo treatment and during terminal differentiation will be measured by Northern blots. The interaction with CHOP in vivo will be demonstrated for these two genes by immunoprecipitation after transfecting Rauscher cells. The functions of these two gene products during growth and differentiation of Rauscher cells stimulated by Epo will be evaluated using established methods following overexpression of these two proteins. The results from this work are expected to advance our understanding of how Epo regulates the growth and differentiation of erythroid cells.